The legitimacy or not depends on the final language and the transcription system used. Some systems transcript the final with he as -ah (Deborah, Noah, Sarah...), others transcript it as -a (Debora, Noa, Sara...), others as -à (Deborà, Milcà, Tirsà, Noà, Sarà...), etc. Even in languages where two systems coexist because both suit the final language, it is usually more common a form because of the tradition.

In the specific case of Noa/Noah, both forms are legit (as is Noà) just as Noah/Noé/Noè are legit forms from the hebrew N-.H.